The present invention relates generally to an exposure apparatus that transfers a pattern of a mask (reticle) onto an object such as a single crystal substrate for a semiconductor wafer and a glass plate for a liquid crystal display (“LCD”), and more particularly to an exposure apparatus that exposes an object using a light with a wavelength of 20 nm or less in a reduced or vacuum environment. The present invention is suitable for an exposure apparatus that uses an extreme ultraviolet light (EUV light) (referred to as an “EUV exposure apparatus” hereinafter).
Along with the recent demands on finer processing and improved economical efficiency, the further improvement of resolution and productivity of the projection exposure apparatus has been increasingly required. In the improvement of resolution, shortening the wavelength of exposure light is general, and recently, an EUV exposure apparatus using EUV light with a wavelength of 10 to 15 nm has been proposed. The EUV light is easily absorbed by air and helium etc., a conventional EUV exposure apparatus accommodates an optical system, mask and object in a vacuum chamber, and exposes with the inside maintained to a vacuum or reduce environment (referred to as only a “vacuum environment” hereinafter).
However, when the mask and object are carried into and carried out of the vacuum chamber, an atmosphere flows into the chamber and the vacuum environment is broken. In addition, it takes a long time to form again a predetermined vacuum environment by evacuating the vacuum chamber. Moreover, organic matters generated from a resist on the object contaminate the optical system during exposure. The contaminated optical system causes various problems, such as a decreased light intensity and throughput, a non-uniform distribution, and a lower resolution etc.
An EUV exposure apparatus that divides the vacuum chamber into plural areas (accommodating parts) and accommodates the mask, object and optical system in different accommodating parts has been proposed (see, for example, Japanese Patent No. 2,691,865 and Japanese Patent Application, Publication No. 2003-332214). The separate accommodating parts enable, for example, the accommodating part that accommodates the optical system to maintain the vacuum environment even when the object is carried out of the vacuum chamber to exchange the object. As a result, after the object is exchanged, only the accommodating part that accommodates the object may be evacuated. Therefore, a time period necessary to form a predetermined vacuum environment shortens, and the optical system is protected from contaminations during exposure.
However, Japanese Patent No. 2,691,865 arranges a light-transmitting thin film window between the accommodating parts, and causes the decreases of the light intensity and throughput because the thin film window absorbs the exposure light. An exposure apparatus of Japanese Patent Application, Publication No. 2003-332214 discloses a pressure difference formed between the accommodating parts. However, it requires to control an interval between a connecting part that partitions two accommodating parts and the object to 20 μm or less for a desired pressure difference, and the control over the pressure difference is difficult. Moreover, Japanese Patent Application Publication No. 2003-332214 sets a vacuum level of the accommodating part for the optical system to 1×10−5 Pa or less (paragraph number 0019) and a vacuum level of the accommodating part for the object and mask to 1×10−4 Pa or more (paragraph number 0020) in one example of the pressure difference. However, the inventors have discovered that this pressure condition is insufficient to improve both the resolution and productivity.
In other words, when carbon molecules such as hydrocarbon, remain on an exposure optical path, the carbon adheres to a surface of the optical element due to the irradiated light, and absorbs the EUV light, causing decreased reflectivity. Such carbon originates in an escape gas from a driving mechanism that drives the object and the mask. The prior art does not propose any pressure controls to prevent the carbon adhesion.